Influence of benomyl and prometryn on the soil microbial activities and community structures in pasture grasslands of Slovakia

Abstract

The effects of pesticides (a herbicide and a fungicide) on the microbial community structure and their activity were analyzed in soil from four alpine pasture grasslands in Slovakia. Specifically, the effects of the herbicide, Gesagard (prometryn active ingredient), and fungicide, Fundazol 50 WP (benomyl active ingredient), on the microbial respiration activity (CO₂ production), the numbers of selective microbial physiological groups (CFU.g⁻¹) and the structure (relative abundance) of soil microbial communities [(phospholipid fatty acid (PLFA)] were analyzed under controlled laboratory conditions. All treatments including the treatments with pesticides increased (statistically significantly) the production of CO₂ in all fields during 21 days of incubation and posed a statistically insignificant negative influence on the numbers of the observed physiological groups of microorganisms. The significantly negative influence was evaluated only in the numbers of two physiological groups; spores of bacteria utilizing organic nitrogen and bacteria, and their spores utilizing inorganic nitrogen. A shift in the microbial composition was evident when the PLFA patterns of samples from different sites and treatments were compared by the Principal Component Analysis (PCA). According to the second component PCA 2 (15.95 %) the locations were grouped into two clusters. The first one involved the Donovaly and Dubakovo sites and the second one contained the Velka Fatra and Mala Fatra locations. The PLFA composition of the soils showed important changes after the treatment with pesticides according to PCA 1 (66.06 %). Other treatments had not had a significant effect on the soil microbial community with the exception of the population of fungi. The lower relative abundance (significant effect) of Gram-positive bacteria, actinomycetes and general group of bacteria were determined in samples treated by the herbicide Gesagard. The application of fungicide Fundazol decreased (statistically significantly) the relative abundance of actinomycetes and general group of bacteria and paradoxically increased the population of fungi.

Keywords:

• Pesticides
• microbial community structure
• microbial respiration
• abundance of microorganisms
• PLFA analysis

Acknowledgement

The authors would like to thank Jim A. Harris and M. Pawlett for their theoretical and practical assistance with PLFA analysis. This research was partly supported by a grant of the School of Applied Sciences, Cranfield University and the Slovak grant agency, VEGA No. 1/3459/06, VEGA no. 1/0404/09 and KEGA No. 3/6228/08. We thank the professional translator Mrs. Emily Heinz Vargic for language corrections of the manuscript and two anonymous reviewers provided valuable comments on the manuscript.